juan_gandhi | Entries tagged with scala

scala> def f(x:String) = null
f: (x: String)Null

scala> Some("abc") map f
res3: Option[Null] = Some(null)

(from Predef:)

  sealed abstract class <:<[-From, +To] extends (From => To) with Serializable
  private[this] final val singleton_<:< = new <:<[Any,Any] { def apply(x: Any): Any = x }
  implicit def conforms[A]: A <:< A = singleton_<:<.asInstanceOf[A <:< A]

Funny. Almost obvious. And interferes with my plans to pass an implicit argument that has an implicit value of an identity function. Because it clashes with "conform", and if I shadow "conform", nothing will compile in that class.

hocon per se is a good stuff; but Typesafe's implementation, Config, is not something I feel happy with.

First, it is JAVA!!!!
Second, where's "getOrElse"? getInt could have a default value, right? Or a default Option value, which is better. Or have a lift that would be returning an option
Third, how about ++ and the like?
Fourth, what is this:


public enum ConfigValueType {
    OBJECT, LIST, NUMBER, BOOLEAN, NULL, STRING
}

This is also funny:

    @Override
    public Long getMilliseconds(String path) {
        long ns = getNanoseconds(path);
        long ms = TimeUnit.NANOSECONDS.toMillis(ns);
        return ms; 
    }

    @Override
    public Long getNanoseconds(String path) {
        Long ns = null;
        try {
            ns = TimeUnit.MILLISECONDS.toNanos(getLong(path));
        } catch (ConfigException.WrongType e) {
            ConfigValue v = find(path, ConfigValueType.STRING);
            ns = parseDuration((String) v.unwrapped(), v.origin(), path);
        }
        return ns;
    }

In short, I'm thinking of abandoning it. Might make sense to write our own stuff, I don't know. So far my Props work well.

Tweaked it a little bit... seems like cannot make it smaller any further; pity.

https://gist.github.com/vpatryshev/ca5a1bfdaf00d2481a0c

deep copy done easily

object Example {
  trait Nested[A] { def dup: A => A }
  object Nested {
    implicit def nestedAnything[A] = new Nested[A] { def dup = identity }
    implicit def nestedArray[A](implicit ev: Nested[A], mf: Manifest[A]) = 
      new Nested[Array[A]] { def dup = _ map ev.dup }
  }
  def deepDup[A](aa: Array[A])(implicit ev: Nested[Array[A]]) = ev dup aa
}

scala> val a = Array(Array(1,2,3), Array(4,5,6), Array(7,8))
a: Array[Array[Int]] = Array(Array(1, 2, 3), Array(4, 5, 6), Array(7, 8))
scala> val c = deepDup(a)
c: Array[Array[Int]] = Array(Array(1, 2, 3), Array(4, 5, 6), Array(7, 8))
scala> a(0)(0)=9; c // it's a copy, not a reference
res0: Array[Array[Int]] = Array(Array(1, 2, 3), Array(4, 5, 6), Array(7, 8))

questions? improvements?

scala> import collection.mutable.Queue
import collection.mutable.Queue

scala> val m: Map[Int, Queue[Int]] = Map().withDefaultValue(Queue[Int]())
m: Map[Int,scala.collection.mutable.Queue[Int]] = Map()

scala> m(0)
res0: scala.collection.mutable.Queue[Int] = Queue()

scala> m(0).enqueue(1)

scala> m(1)
res2: scala.collection.mutable.Queue[Int] = Queue(1)

"abc" map { case 'a' => "A"; case x => x }

case classes in Scala have a method copy

Neat, nice, nifty!

Now the question is: why would one need it, in case the class is immutable?!

This is why

  case class Person(first: String, second: String)
  val p1 = Person("John", "Waters")
  val p2 = p1.copy(first="James")

http://www.programmingusingscala.net/home/chapters

Many chapters represented as video talks by the author.

https://github.com/aztek/master-thesis

Mark Hamsra's talk

Benchmarking Scala against Java

funny eh

Seems like scala people look down at exceptions... but see. The difference between an error message and an exception is that an exception tells you where the error happened. I actually use it in pretty unusual places, like this:

def jsREPL(implicit prompt:String = "type your js") {
  val here = Thread.currentThread().getStackTrace()(3)
  println(s"$prompt [${here.getFileName}:${here.getLineNumber}]: ")
  Source.fromInputStream(System.in).getLines.takeWhile(!_.isEmpty) foreach {
    s => println(tryOr(runJS(s), (_:Exception).getMessage))
  }

What I want to say: if we, in Scala, had a habit of passing around exceptions, instead of plain text, it would be pretty helpful.

Thinking about it.

Scala existential types, are they factortypes, are they not? Coequalizers, function images, like that.

can anybody please please please add val to JavaScript?!!!!!

Сегодня приходили за котятами - а я не смог поймать. Они сделали подкоп под кухню, и прячутся туда если чо.

О как сложна жизнь.

Другая тема - это надо что-то делать с кодом типа такого:

 result match {
   case Good(something) =>
     something match {
       case arr: Array[(String, String)] => println(s"aint that something ${arr mkString ", "})
       case x => error(s"bad, bad response pretending to be good: $result")
     }
   case noGood => error(s"no good! $result)
 }

This still causes a (rightful) warning, and I don't see (yet) how I can fix it all without being absolutely stupid. It frustrates me, yes. I don't even see a monadic pattern here... neither an app functor. Bad, bad.

  def tryOr  [T](eval: =>T, onError: Exception => T) =
    try { eval } catch { case e: Exception => onError(e) }

  def tryOr  [T](eval: =>T, orElse: T) =
    try { eval } catch { case e: Exception => orElse }

  def attempt[T](eval: =>T): Option[T] = tryOr(Option(eval), None)

  class BetterArray[T](array: Array[T]) {
    def get(i: Int): Option[T] = attempt(array(i))
    def getOrElse(i: Int, defaultValue: T) = get(i) getOrElse defaultValue
  }

  implicit def elementOf[T](array: Array[T]) = new BetterArray[T](array)

questions?

Current Mood: creative

Идея: есть джавный java.util.ArrayList, древний как доткомовский бум. А мы хочем функтор, но не можем написать ArrayList extends Functor; ну дык... дык и хер с ним; мы ж инженеры. В Скале можно. А зачем? А чтобы писать arrayList.map(someting=>something)
И в продакшен. Мы же инженеры!

gist

Могу написать подробные комментарии, если интересно.

      val out = new FileOutputStream(myFile).getChannel
      val in: InputStream = sampleResourcePdfBSBCTX.openStream
      val ch = Channels.newChannel(in)
      try {
        while (true) {
          val nBytes = in.available
          out.transferFrom(ch, out.position, nBytes)
          out.position(out.position + nBytes)
        }
      } finally { out.close() }
      val text = PDF.extractTextFromImagesHiddenInPdf(pdf)
      text contains "Claim No.: 30l8507l5lSOX" mustBe true
    }
  }

scala cake pattern in details

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Juan-Carlos Gandhi

patryshev.com

November 2025

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Entries tagged with scala

scala option map fuckup

(not so) dirty secrets of Scala

hocon

v2

nice scala

mutability: butterfly effect

funny discovery

just learned

videobook, kind of

о, Котельников выложил свою дипломную работу

spark and shark

oh, scala performance...

about exceptions in jvm

now tell me...

a prayer

котята, блин

some obvious stuff

а вот простой пример как из джавного ArrayList сделать функтор на коленке

dumping stuff from stream to file fast

good reading